The present invention relates to a method of converting a frame of bit stream on the basis of a pointer conversion and an apparatus of using same. More particularly, it relates to a method of phase-converting a frame by using a pointer indicating the front position of data in a frame when a phase synchronization is carried out in a time division multiplexing digital signal transmission system.
In a transmission network in which a time division multiplexing digital signal transmission is carried out, apparatuses (network nodes or interfaces) each of which converts a signal(s) on an input line(s) to a signal(s) having a signal form(s) adaptive to an output line(s), are required. The fundamental function of that conversion is a frame signal phase conversion. New methods for carrying out the phase conversion among those methods in which a pointer in each frame is provided to indicate the front position of multiplexed data in the frame, are known. For example, a Synchronous Optical Network (SONET), described in Technical Advisory, TA-TSY 00253, published on May 2, 1987 by Bell Communication Research Institute, is known as one of those new methods.
In the method for carrying out the phase conversion of the frame by using the pointer, each frame in a communication signal is comprised of a frame synchronous signal, a pointer and an overhead signal, which are arranged in fixed positions in the frame, and data arranged in positions other than the fixed positions in the frame. The number of bytes from the position arranged the pointer to the front position of the data, i.e., an offset value, is written in a pointer storage portion in the frame. Unless the value of the pointer is changed, the front of the data is located at a same offset position in each frame.
When the frame including the pointer is received and data are to be rearranged in a new frame which is different from the received frame, a value of the pointer must be changed to accommodate the new frame. This method for carrying out the phase conversion of the frame signal by using the pointer does not suffer from a retardation of the data signal process, occurred in the prior art methods in which the conversion is carried out on the basis of the frame synchronous signal, and enables a circuit arrangement to be simplified in an apparatus such as a line exchanger.
A recommendation of an International Standard of the method for carrying out the phase conversion of the frame signal by using the pointer had been enacted, however specific methods and specific apparatuses for carrying out that phase conversion have not yet been established.